求救！下载器与Pickit2连接No device found

新手刚买的单片机开发板，用的是pic16F877A。卖家发货给我的时候下载器是测试过有用的，但是到我这里宿舍三台电脑都出现同样的问题。只连接下载器的话，软件显示no device found
把板子也接上提示错误代码ID=3FE0

用MPLAB8.73烧录的时候显示
Initializing PICkit 2 version 0.0.3.63
Found PICkit 2 - Operating System Version 2.32.0
Target power detected ( 4.99V)
PKWarn0003: Unexpected device ID:  Please verify that a PIC16F877A is correctly installed in the application.  (Expected ID = 0xE20, ID Read = 0x0)
PICkit 2 Ready

检查供电。断电，重插，重启